The present invention relates to improvements in a wire electrical discharge machine for machining a workpiece by electric discharge energy by supplying machining electric power between a wire electrode and the workpiece.
FIG. 8 is a schematic diagram illustrating a conventional wire electrical discharge machine, in which reference numeral 1 denotes a wire electrode; 2, a workpiece, 3, a wire bobbin; 4, a main tension pulley for imparting tension to the wire electrode 1; and 5, a braking motor for causing the main tension pulley to produce torque. Numerals 6a and 6b denote wire guides respectively provided above and below the workpiece 2; 7a and 7b, working fluid nozzles respectively provided above and below the workpiece 2, and 8a and 8b, feeders for supplying machining electric power to the wire electrode 1. Numeral 9 denotes a power supply unit for machining; 10, a wire-electrode-traveling roller; 11, a wire-electrode-traveling motor; 12, a wire-electrode collection box; and 13, a braking motor for pretensioning for causing the wire bobbin to generate torque. Numerals 14a, 14b, and 14c denote guide pulleys. In addition, arrow A in the drawing indicates the traveling direction of the wire electrode 1.
In such a conventional wire electrical discharge machine, as the wire-electrode-traveling roller 10 is driven-by the wire-electrode-traveling motor 11, the wire electrode 1 is pulled out from the wire bobbin 3. In the main tension pulley 4 and the wire bobbin 3, predetermined tensions are applied to the wire electrode 1 by the braking motors 5 and 13. In the state in which these predetermined tensions are applied, the wire electrode 1 travels in the direction of arrow A in the drawing while maintaining a predetermined speed. The wire bobbin 3 rotates about a wire bobbin shaft as the wire electrode 1 travels. The wire electrode 1 is wound around the wire bobbin 3, and is continuously pulled out from the wire bobbin 3. In conjunction with the traveling of the wire electrode 1, machining electric power is supplied to the gap between the wire electrode 1 and the workpiece 2 from the machining power supply unit 9 through the feeders 8a and 8b, and a working fluid is supplied to the gap through the working fluid nozzles 7a and 7b, with the result that electric discharge occurs. As the wire electrode 1 and the workpiece 2 are relatively moved in a predetermined machining direction by an unillustrated drive mechanism, the machining of the workpiece 2 progresses.
In such wire electrical discharge machining, a substantial portion of the wire electrode 1 facing the machining direction is worn due to the discharge. Accordingly, since the frequency of disconnection of the wire electrode 1 increases, there has been a problem in that the machining rate declines appreciably.
In addition, the wear of the wire electrode 1 has a large effect on the machining accuracy as well. Namely, since the wear of the wire electrode 1 progresses while the wire electrode 1 is traveling from an upper portion to a lower portion of the workpiece 2, there has been a problem in that taper-like errors occur on the machined surface of the workpiece 2 with respect to the traveling direction of the wire electrode 1. Such taper-like errors become noticeable particularly in cases where the thickness of the workpiece 2 is large.
FIG. 9 is a partial cross-sectional view illustrating a wire-electrode loading mechanism in a wire electrical discharge machine disclosed in JP-A-63-2630 for the purpose of resolving the problems of the above-described conventional art. In the drawing, reference numeral 1 denotes the wire electrode; 3, a wire bobbin; and 14a, a guide pulley. Numerals 15a and 15b denote bearings, and numeral 16 denotes a rotating jig; 17, a bearing; 18, a rotating motor; 18a, an output shaft of the rotating motor 18; and 19, a fixing base. The wire bobbin 3 is supported by the rotating jig 16 by means of the bearings 15a and 15b so as to be rotatable about a xcex2 axis in the drawing. Further, the rotating jig 16 is connected to the output shaft 18a of the rotating motor 18.
The overall construction of the wire electrical discharge machine having the wire-electrode loading mechanism having the arrangement shown in FIG. 9 is similar to that shown in FIG. 8, and corresponds to an arrangement in which the wire bobbin 3, the braking motor 13, and the like in FIG. 8 are replaced by FIG. 9. It should be noted, however, that a motor corresponding to the braking motor 13 shown in FIG. 8 is not present in FIG. 9. Accordingly, in order to be provided with functions utterly identical to those of the overall construction shown in FIG. 8, it is necessary to add the braking motor 13 to, for example, the xcex2 axis shown in FIG. 9
In FIG. 9, if the wire electrode 1 travels (in the direction of arrow A in the drawing), the wire bobbin 3 rotates about the xcex2 axis (in the direction of arrow B in the drawing), and the wire electrode 1 wound around the wire bobbin 3 is pulled out from the wire bobbin 3. In conjunction with the traveling of this wire electrode 1, the wire bobbin 3 is rotated about an xcex1 axis (in the direction of arrow C in the drawing) by the rotating motor 18 to impart rotation to the wire electrode 1, thereby making it possible to disperse the wear of the wire electrode 1 at the time of wire electrical discharge machining. Therefore, there is an advantage, among others, in that the machining accuracy of the workpiece can be improved.
In the arrangement of the wire-electrode loading mechanism such as the one shown in FIG. 9, the rotating motor 18 used exclusively for imparting rotation to the wire electrode 1 is required in addition to the braking motor (e.g., 13 in FIG. 8) for applying tension to the wire electrode 1. In addition, since there is a need to rotate the entire wire bobbin 3 about the xcex1 axis, the load inertia of the rotating motor 18 is large, so that the rated output of the rotating motor 18 and the capacity of the allowable rated load and the like of machine elements such as the bearing 17 are required to be large. Hence, there has been a problem in that an increase in cost is large, and this arrangement is not practical.
The present invention has been devised to overcome the above-described problems, and its object is to obtain a wire electrical discharge machine which makes it possible to disperse the wear of the wire electrode and improve the machining rate and machining accuracy.
Another object is to obtain a wire electrical discharge machine which makes it possible to suppress an increase in cost without requiring the provision of a new motor for imparting rotation to the wire electrode, and which is highly reliable and is practical.
The wire electrical discharge machine in accordance with the invention is a wire electrical discharge machine for machining a workpiece by electric discharge energy by causing discharge to occur between a traveling wire electrode and the workpiece, comprising: a wire bobbin with the wire electrode wound therearound; fixing means for fixing the wire bobbin so that the wire bobbin does not rotate; guiding means for supporting the wire electrode; wire-electrode rotating means for supporting the guiding means and for pulling out the wire electrode from the wire bobbin and rotating the wire electrode about the wire bobbin; and driving means for driving the wire-electrode rotating means.
In addition, in the wire electrical discharge machine in accordance with the invention, the driving means is a braking motor for imparting predetermined tension to the wire electrode.
In addition, in the wire electrical discharge machine in accordance with the invention comprises: sliding means for supporting the guiding means slidably with respect to the wire-electrode rotating means, in correspondence with a winding position of the wire electrode on the wire bobbin.
In addition, the wire electrical discharge machine in accordance with the invention is a wire electrical discharge machine wire electrical discharge machine for machining a workpiece by electric discharge energy by causing discharge to occur between a traveling wire electrode and the workpiece, comprising: a wire bobbin around which the wire electrode is wound in advance with in a state in which rotation in a twisting direction is continuously imparted to the wire electrode, and which is supported in such a manner as to be rotatable in a direction in which the wire electrode is pulled out.
Since the wire electrical discharge machine in accordance with the invention is constructed as described above, the following advantages are offered.
The wire electrical discharge machine in accordance with the invention is capable of dispersing the wear of the wire electrode and improving the machining rate and machining accuracy.
In addition, the wire electrical discharge machine in accordance with the invention is capable of improving the reliability.
In addition, the wire electrical discharge machine in accordance with the invention is capable of suppressing an increase in cost.